The predominate blowing agent for the generation of thermoplastic foam extrudates on a commercial basis has been fluorocarbons, for example, trichlorofluoromethane and dichlorofluoromethane. As a result of ecological studies, fluorocarbons have been determined to be an undesirable pollutant for the atmosphere. Accordingly, ways are being sought to eliminate or materially reduce the utilization of fluorocarbons for all purposes wherever possible. A significant area in which to eliminate fluorocarbons from manufacturing processes is in the generation of thermoplastic foam extrudates such as thermoplastic foam sheeting and the like.
In the process of eliminating fluorocarbons, it becomes apparent that if chemical blowing agents can also be successfully eliminated and only harmless ingredients utilized as the blowing agents, then the manufacturing processes for foamed thermoplastic extrudates would become more ecologically sound.
Natural gases such as air, pure nitrogen or pure carbon dioxide, all of which have predictable and acceptable effects on the ecology, would be the most desirable blowing agents. In addition to these gases, water, since it would become vaporized in contact with molten thermoplastic masses in an extruding line or the like, is also a prime candidate for an ecologically sound blowing agent.
It is therefore an object of the invention to supplant Freon as a blowing agent for foamed thermoplastic extrudates and the like.
Another object of the present invention is to provide a new and novel method and apparatus for injecting air, nitrogen, carbon dioxide, water and/or combinations of these into an extrusion system configuration as blowing agents to produce foamed thermoplastic extrudate from that extrusion system.
Another object of the present invention is to reduce the cost of producing foamed thermoplastic extrudates.
Still another object of the present invention is to provide foamed thermoplastic extrudates of enhanced quality.
Yet another object of the present invention is to provide a new and novel combination of gases and/or water and/or other ingredients as the blowing and nucleating agents for the production of foamed thermoplastic extrudates and the like, thereby totally supplanting and eliminating the need for fluorocarbons in the production of such products.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawings which relate to several preferred embodiments of the invention.